Melaleuca L.

Scientific Description

Common name. Paperbarks. Family Myrtaceae.

Includes M. viminalis (Sol. ex Gaertner) Byrnes.

Habit and leaf form. Trees, or shrubs; evergreen; bearing essential oils. Plants with neither basal nor terminal concentrations of leaves; to 1–25 m high. Leptocaul. Helophytic to xerophytic. Leaves minute to large; alternate, or opposite, or whorled (rarely); spiral; decussate; leathery; petiolate to sessile; gland-dotted; aromatic, or without marked odour; edgewise to the stem, or with ‘normal’ orientation; simple; peltate, or not peltate; epulvinate. Leaf blades dorsiventral, or isobilateral, or centric; entire; flat, or rolled, or solid; terete, or semi-terete; linear, or lanceolate, or oblong, or ovate; linear, or ovate, or obovate, or elliptic, or triangular; 1–9 -nerved (or obscure); pinnately veined, or parallel-veined, or one-veined; cross-venulate, or without cross-venules; cordate, or attenuate at the base, or cuneate at the base (or truncate or obtuse). Mature leaf blades adaxially glabrous, or pubescent, or woolly; abaxially glabrous, or pubescent, or woolly. Leaves without stipules; without a persistent basal meristem. Stem anatomy. Secondary thickening developing from a conventional cambial ring.

Reproductive type, pollination. Fertile flowers hermaphrodite, or hermaphrodite and functionally male, or hermaphrodite, functionally male, and functionally female. Unisexual flowers present, or absent. Plants hermaphrodite, or andromonoecious, or polygamomonoecious. Entomophilous, or ornithophilous. Pollination mechanism unspecialized.

Inflorescence and flower features. Flowers aggregated in ‘inflorescences’. Inflorescence few-flowered, or many-flowered. Flowers in spikes (forming ‘bottlebrushes’), or in heads, or in racemes. Inflorescences simple, or compound. The terminal inflorescence unit cymose. Inflorescences terminal, or axillary; of monads, dyads or triads in dense heads or spikes; with involucral bracts, or without involucral bracts; pseudanthial. Flowers shortly pedicellate to sessile; bracteate, or ebracteate. Bracts persistent, or deciduous. Flowers bracteolate, or ebracteolate (bracteoles 2 or 3). Bracteoles persistent, or deciduous. Flowers small to medium-sized; regular; 5 merous; cyclic. Free hypanthium present; campanulate, or turbinate, or urceolate, or tubular, or globose (or barrel-shaped); extending beyond ovary; adnate to ovary at base. Hypogynous disk present. Perianth with distinct calyx and corolla, or petaline (in M. cornucopiae); 5, or 10 (usually); 1 -whorled, or 2 -whorled; isomerous. Calyx present, or absent; 5; 1 -whorled; polysepalous, or gamosepalous (depending on interpretation); lobed; imbricate, or valvate; exceeded by the corolla (usually very small); regular; not persistent, or persistent (rarely). Sepals ovate, or triangular. Calyx lobes ovate, or triangular. Corolla present; 5; 1 -whorled; polypetalous; imbricate; regular; white, or yellow, or red, or pink; persistent, or deciduous. Petals elliptic, or ovate, or obovate, or orbicular; shortly clawed, or sessile. Corolla members entire. Fertile stamens present, or absent (female flowers, rare). Androecial members indefinite in number. Androecium 15–450. Androecial members branched, or unbranched (rarely). Androecial sequence determinable, or not determinable. Androecial members if ‘many’, maturing centripetally; free of the perianth; all equal, or markedly unequal; coherent (bundled to form staminal claws, sometimes with free stamens in M. nervosa and M. stenostachya); 5 - adelphous, or 5–10 - adelphous (the claws sometimes divided to their bases), or 1 - adelphous (when the filaments are confluent into a ring, as in M. viminalis var. minor). The androecial groups opposite the petals. Stamens 15–450; attached on the rim of the hypanthium; becoming exserted (exceeding the petals); all more or less similar in shape; triplostemonous to polystemonous; alternisepalous (usually), or alternisepalous and oppositisepalous; all opposite the corolla members, or both opposite and alternating with the corolla members (rarely); erect in bud, or inflexed in bud. Filaments hairy, or glabrous. Anthers dorsifixed; versatile; dehiscing via longitudinal slits; introrse; tetrasporangiate; appendaged, or unappendaged. Fertile gynoecium present, or absent (male flowers, unusual). Gynoecium 3 carpelled. The pistil 3 celled. Gynoecium syncarpous; eu-syncarpous; partly inferior to inferior. Ovary plurilocular; 3 locular. Ovary summit hairy, the hairs not confined to radiating bands. Epigynous disk present, or absent. Gynoecium stylate. Styles 1; simple; from a depression at the top of the ovary; apical; persistent, or deciduous; hairy, or hairless. Stigmas 1; capitate, or peltate (or very small). Placentation axile (-median). Ovules 4–230 per locule; ascending; non-arillate; anatropous.

Fruit and seed features. Fruit subsessile to sessile; persistent (and often partially immersed in the stem); non-fleshy; dehiscent; a capsule (3-valved, enclosed in the more or less woody hypanthium). Capsules loculicidal. Fruit 3 celled; few to many seeded. Seeds non-endospermic; linear; wingless. Cotyledons 2; obvolute. Embryo straight.

Geography, cytology, number of species. Native of Australia. Not endemic to Australia. Australian states and territories: Western Australia, South Australia, Northern Territory, Queensland, New South Wales, Victoria, Australian Capital Territory, and Tasmania. Northern Botanical Province, Eremaean Botanical Province, and South-West Botanical Province.

Etymology. From the Greek for "black" and "white"; refers to the black trunk and white branches of some Asian species.